IE61742B1 - Glucuronic acid derivatives of opioid antagonists - Google Patents

Description

GLUCURONIC ACID DERIVATIVES OF OPIOID ANTAGONISTS BACKGROUND OF THE INVENTION This invention relates to glucuronic acid derivatives of opioid antagonists, and more particularly to the use of such compounds for the manufacture of a medicament for the treatment of localized symptoms with a minimum of systemic effects.

Opioid antagonists are a well-known class of drugs which can be used to prevent or promptly reverse the effects of morphine-like opioid agonists. See Goodman and Gilman's The Pharmacological Basis of Therapeutics, Sixth Edition, pp. 521-525. It is known that the opioid antagonist, naloxone, is converted by the human body to the glucurcnide form, although no use for this form of naloxone has been found before the present invention. Of particular interest among the known opioid antagonists is nalmefene, which was first identified and claimed in U.S. Patent No. 3,814,768 as 6-methylene-6-desoxy-N-cyclopropylmethyl“14hydroxydi hydronormorphine.

The constipating effect of opioids is the oldest known effect of these drugs. Indeed constipation is the most troubling side effect when opioid drugs are employed to relieve pain. Patients who require opioid analgesics to relieve pain on a chronic basis e.g. cancer victims, suffer severe constipation. Such constipation is also common among opioid addicts, and may even be a problem for those being given opioids on a short term basis, such as patients undergoing surgery.

Sudden withdrawal of opioid drugs following prolonged exposure provokes intestinal hypermotility and diarrhea results. This withdrawal phenomenon of hypermotility and diarrhea is also produced if an opioid antagonist is given after prolonged opioid administration. Thus the opioid can cause hypomotility and constipation, and withdrawal can cause the opposite effect of hypermotility and diarrhea. Hypomotility and hypermotility are dysmoti1ities at the extreme ends of the spectrum of intestinal motility. If an opioid antagonist were administered throughout the period of opioid exposure, intestinal dysmotility at both ends of the spectrum could be forestalled.

Attempts have been made to provide opioic a'tagonists that would i relieve the constipating effect of exogenous opioids without antagonizing e analgesic effect. This is particularly important for chronic users or addicts since systemic antagonism can cause severe withdrawal symptoms 5 mediated by the central nervous system. One class of compounds which has been investigated for this purpose are the quaternary ammonium derivatives of known narcotic antagonists (US Patent 4^176,,157)., The quaternary antagonists antagonize opioid induced intestinal hypomotiiity at lower , doses than are required to antagonize opioid induced analgesia. The ^0 selective antagonism,, i.e, more effective on intestinal hypomotiiity than on central nervous system analgesia, occurs because quaternary compounds are highly charged. The blood brain barrier iKpedes passage of highly charged drugs. Thus,, the quaternary ammonium antagonists have more limited access to the opioid receptors in the central nervous system (CHS) that mediate analgesia than they do to the opioid receptors in the intestine that mediate hypomotiiity.

It is doubtful however that the quaternary ammonium antagonists will provide a practical solution to the clinical problem of the constipating effects of opioid analgesics. It has been knowri since the work of Eddy in 1933 (J. Pharmacol. Exp. Therap.., 1967, 157:155-195) that .quaternarization was a means of directing cpioids away from the CNS and toward the intestine. Yet no clinically useful quaternary opioid antagonist is available to patients. The failure of such a drug to emerge in therapeutics is likely related to the toxic effects on the autonomic nervous system that are known to occur with quaternary ammonium drugs.

In addition to relieving the constipatir.z effects of exogenous opioids, the present invention is also directed to preventing endogenous opioids from exacerbating intestinal dysmoti'iity of irritable bowel syndrome. In the last decade it's been discovered that the body produces its own opioids. The endogenous opioids are called endorphins and enkephalins. There is an abundance of endogenous opioids and opioid receptors in the intestinal tract. From the work of Kreek et al. (Lancet 1983 1:262) it appears that such endogenous opioids contribute to intestinal dysmotility. Kreek et al. have shown that the opioid antagonist - 2 naloxone relieves constipation even though the patients have not been exposed to an exogenous opioid.

Irritable bowel syndrome is a form of intestinal dysmotility well Miown to gastroenterologists. The syndrome is characterized by pain as well as alternating constipation and diarrhea. The endogenous opioids may exacerbate the syndrome. The hypomotility and constipation phase of the syndrome could be the result of an excessive endogenous opioid influence,, while the hypermotility and diarrhea could result from an abrupt cessation of endogenous opioid activity. In irritable bowel syndrome we believe that there is an exaggerated cyclic effect of the endogenous opioids on the intestines. During the upphase of the cycle the intestines can be immobilized and become physically dependent upon the endogenous dpioids. During the down phase of the cycle the intestines can go into withdrawal„ and thus become hypermotile and produce diarrhea. Pain can result from both constipation and diarrhea.

It appears then that a cycling auto-addiction and withdrawal is an important contributor to irritable bowel syndrome. Just as the continued presence of an opioid antagonist would prevent the addiction or physical dependence of the intestines to exogenous opioids, an antagonist should similarly prevent the exacerbating influence of cycling endogenous opioids on the intestine.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an opioid antagonist which has a local therapeutic effect in the intestinal tract with a minimum of systemic effects, particularly central nervous system (CNS) effects.

In accordance with the above objects of this invention, glucuronic acid derivatives of opioid antagonists are provided for the treatment of intestinal dysmotil ity with a minimum of systemic effects. Nalmefene glucuronide has been found particularly useful for achieving the objects of '$ invention.

DETAILED DESCRIPTION Thjs invention uses the D-D-glucuronic acid derivatives of opioid antagonists for colon specific drug delivery. These compounds are given by the following general formula: Wherein R^ is either =0 or =CHgS and R,? is allyl or cyclopropyImethyl.

Three compounds of particular interest are nalmefene -3β -D-glucuronide (Rj is =CHg and Rg is cyclopropylmethyl), naloxone -3S -D-glucuronide (R( is =0 and Rg is allyl) and naltrexone -32 -D-glucuronide (Ra is =0 and Rg is cyclopropylmethyl).

In accordance with the present inventions it has been found that these glucuronide compounds have little or no opioid antagonistic effect unless they are enzymatically cleaved to yield the free antagonist. For example: Nalmefene-3S -D-glucuronide + β-glucuronidase ·* Nalmefene + glucuronic acid β-glucuronidase is a naturally occuring enzyme which is present in the bacterial flora of the lower intestinal tract, particularly in the colon.

Therefore the compounds of this invention provide a means of specific delivery of an opioid antagnoist to the lower intestinal tract. Opioid antagonist activity in the body outside the intestine is avoided because glucuronic acid derivatives are poorly absorbed and rapidly eliminated in the urine. Further, the glucuronides do not encounter S-glucuronidase outside the intestine.

' After liberation of the aglycone antagonist in the lower intestinal tract, smal) amounts of this aglycone antagonist could be absorbed into the Portal circulation. However as the aglycone antagonist passes into the portal blood and through the liver it will be reconverted to its S-D-glueuronide conjugate by hepatic glucuronyl transferase. Therefore no significant amount of active antagonist will reach the systemic circulation.

An analysis of the blood and urine of rats treated with nalmefene •orally showed that the concentration of nalmefene glucuronide is about 100 fold higher than is tha concentration of free nalmefene. Thus nalmefene is almost totally biotransformed as a result of “first-pass metabolism when administered orally. Such a high degree of biotransformation is common for this type of drug. However it was discovered that the relative concentrations of free nalmefene and nalmefene glucuronide in the feces of these animals were in marked contrast to the blood and urine. Whereas the ratio of nalmefene to nalmefene glucuronide in the blood and urine was „ about 1:100, in the feces the ratio was about 3:1. This suggests that some of the nalmefene glucuronide formed from nalmefene as a result of first-pass metabolism in the liver, was excreted via the bile into the intestine and subsequently hydrolysed by intestinal micro flora to yield free nalmefene.

This observation led to developing opioid antagonist drugs with activity confined to the intestine. This intestinal specificity would provide for the following three therapeutic applications: 1) Preventing the unwanted constipation (side effect) caused by opioid analgesic drugs without interfering with the wanted analgesic effect. 2) Treating idiopathic constipation. 3) Treating irritable bowel syndrome.

SYNTHESIS The compounds according to the present invention can be prepared by the reaction of opioid antagonists salts (for example lithium salts) with the appropriate bromosugar followed by alkaline hydrolysis of the protecting groups. These compounds can also be obtained by the Koenigs- 5 Knorr reaction (R.L. Whistler and ILL. Woiironi, 'Metboas in cai uoiiyorate ‘ Chemistry; R.B. Conrow and S. Bernstein, 0. Org. Chem. 1971, (36), 863 and literature cited therein) followed by alkaline hydrolysis.

The present invention is described in more detail by way of the following non-limiting examples. Examples 1 and 2 are synthesis of precursor materials and are described in Bollenback, et al.«, J. Am. Chem. Soc. 1955, (77), 3310.

Example 1. g of D-glucurono-6,3-1actone was added to a solution of 0.11 g of sodium hydroxide in 300 ml of methanol. The mixture was stirred at room temperature for 1 hour and the methanol was then removed under vacuum. The residue was dissolved in 100 ml of pyridine and 150 ml of acetic anhydride was added at 0 C. After 18 hours at 0C the precipitate was filtered and recrystallized from ethanol. 38 g of methyl tetra-O-acetyl-g-D-glueopyran15 uronate was obtained, with M.P. 176.5-178 + 7.668 (c 1» CHCL·).

D *5 Example 2. g of methyl tetra-O-acetyl-B-D-glucopyranuronate was dissolved in 20 ml of 30% hydrobromic acid in acetic acid and the reaction mixture was kept overnight at 0C. The solvent was then removed under vacuum and the residue was dissolved in 25 ml of chloroform. This solution was extracted with cold aqueous sodium bicarbonate and water, dried over sodium sulfate and the solvent was removed under vacuum. The residual syrup was crystallised from ethanol and 4.5 g of methyl(tri-O-acetyl-a-D-glucopyranosyl bromide)-uronate was obtained with M.P. 105-7 C, [α]θ ~ (c 1, CHC13).

Example 3.

To a solution of 2.555 g of nalmefene free base and 0.269 g of lithium hydroxide monohydrate in 11 ml of methanol was added 2.15 g of methyl (tri-O-acetyl-a-D-glucopyranosyl bromide)-uronate. After 30 min at room temperature a solution of 0.430 g of lithium hydroxide in 11 ml of water - 6 was added. After another 30 min the reaction was brought to pH 8 with acetic acid and the unreacted nalmefene was filtered off. The filtrate was evaporated and the residual syrup was chromatographed on a silica gel column with chloroform: methanol = 3:2 as elutant. It was then further purified on an Reform ion-exchange resin with ammonium hydroxide solution as elutant and 0.78 g of nalmefene~3g~D-glucuronide was obtained.

Elemental analysis Calculated for C27^33M%”^H2° Found c H 58.79 6.76 2.54 58.76 6.78 2.53 Example 4.

A solution of 0.397 g of methyl(tri-0-acetyl-a-D-glucopyranosyl bromide)-uronate in 10 ml of toluene was added dropwise over a period of 1 hour to a mixture of 0.17 g of nalmefene free base and 0.172 g of cadmium carbonate in 10 ml of toluene. During the addition, 10 ml of toluene was also removed from the reaction mixture by distillation. Distillation of toluene was continued for another 0.5 hour during which time an equal volume of toluene was added dropwise to the reaction mixture. The inorganic salts were then removed by filtration and the filtrate was evaporated. The residue was chromatographed on a silica gel column with chloroform : methanol = 9:1 as elutant. This gave 0.240 g of methyl (nalmefene-tri»0-acetyl-8~D-glucopyranosid)-uronate.

Example 5.

To the solution of 0.830 g of nalmefene free base and 0.087 g of lithium hydroxide monhydrate in 4 ml of methanol was added 0.7 g of methyl(tri-O-acetyl-a-D-glucopyranosyl bromide)-uronate. After 30 min at room temperature the reaction mixture was brought to pH 8 with acetic acid and the unreacted nalmefene was filtered off. The filtrate was evaporated and the residual syrup was chromatographed on a silica gel column with (I chloroform : methanol = 9:1 as elutant. 0.81 g of methyl(nalmefene-tri30 0-acetyl-3-D-glucopyranosid)-uronate was obtained.

Example 6.

To a solution of 0.81 g of methyl(nalmefene-tri-O-acetylβ-D-glucopyranosid) uronate in 3.6 ml of methanol was added a solution of 0.12 g of lithium hydroxide in 3.6 ml of water. After 30 min at room temperature the reaction mixture was brought to pH 8 with acetic acid and the solvents were removed under vacuum. The residual syrup was purified as in example 3 and 0.41 g of nalmefene-36-D-glucuronide was obtained. This was identical to the product in example 3.

Example 7. Τθ To a solution of 3.7 g of naloxone free base and 0.4 g of lithium hydroxide in 16 ml of water was added 3.26 g of methyl(tri-O-acetylβ-D-glucopyranosyl bromide)-uronate,, After 30 min at room temperature a solution of 0.65 g of lithium hydroxide in 16 ml of water was added. After another 30 min the reaction was brought to pH 8 with acetic acid and the unreacted naloxone was filtered off. The filtrate was evaporated and the residual syrup was crystallized from 95% ethanol and 2.27 g of naloxone-35 -D-glucuronide was obtained.

Elemental analysis C Calculated for CggH^gNO-j^HgO 55.65 Found 55.27 H 6.16 .86 N 2.6 2.54 TEST RESULTS To determine whether nalmefene glucuronide would alleviate morphine-induced hypomotiiity,, the charcoal meal assay method of VJitkin et al. (J. Pharmacol. Ext. Therep.9 133: 4003 1961) was done on 56 mice. The Θ results of the assay are given in Table 1 below. These results show that nalmefene-5-D-glucuronide was as effective as nalmefene in alleviating the depressant effects of morphine on intestinal transit.

R Table 1 Summary of the Results ot the Charcoal Meal Assay3 (Gastrointestial Motility) in Mice Given Nalmefene HCI and Nalmefene- β-D-Glucuronide Percent Meal Group Treatment0_Traveled ± S.E.M, (N) = g of Mice 1 Saline + Saline 68 ± 2 (N=14) 2 Saline + Morphine 28 ± 2 (N=8)c 3 Morphine -s- Saline 31 ± 3 (NS8)C*9 4 Saline * Nalmefene Glucuronide 66 ± 3 (N=8)d 5 Morphine + Nalmefene Glucuronide 58 i 12 (N=5)d’e*h’i 6 Saline * Nalmefene HCI 63 ± 2 (N=8)C 7 Morphine -ϊ- Nalmefene HCI 66 ± 14 (N=5)d’e,T aWitkin et al., JPET 133: 400, 1961.

^The first vehicle or drug listed under Treatment was given 30 minutes. before the second vehicle or drug listed. The results were determined 30 min later. Ail treatments are p.o. end given in a volume of 0.3 ml.

Doses were 10 mg/kg for morphines 15 mg/kg or 2.9 x 10° M/kg for nalmefene glucuronide and 2.9 x 10“° M/kg for nalmefene HCI.

Significantly different (p <0.05) from Saline + Saline controls, d No significant difference compared with Saline + Saline group.

Significantly different (p <0.05) from Morphine + Saline group, f No significant, difference compared with Saline + Nalmefene group. 9 No significant difference compared with Saline Morphine group, h No significant difference compared with Saline + Nalmefene Glucuronide. ΊΝο significant difference compared with Morphine + Nalmefene group.

Group 1 shows that the percentage of the intestinal tract traveled by the charcoal meal when no drug is given (just vehicle control) is 69 s 22. Morphine (groups 2 and 3) reduced the percentage of the intestine traveled bv more than half. τη absence of morphine neither nalmefene (group 6) nor nalmefene glucuronide (group 4) had any significant effect. However both nalmefene (group 7) and nalmefene glucuronide (group 5) protected the intestine against the depressant effect of morphine. In these latter two groups the percentage of intestine traveled was not significantly less than in the group (group 1) where no morphine was present.

Having found that nalmefene-3 0-D-glucuronide was as effective as nalmefene in preventing morphine-induced intestinal hypomoti1ity, experiments were done to determine whether nalmeiene-glucuronide lacked opioid antagonist effect in the central nervous system.

The Rapid Quantitative In Vivo Assay for Narcotic Antagonist cf Katovich et al. (Substance and Alcohol Actions/Misuse, vol 5: 87095, 1984) vas used. This assay is based on the extreme sensitivity of opioid-dependant animals to narcotic antagonists. Injection of these 5 animals with a narcotic antagonist produces severe central nervous system withdrawal signs. One of these signs is an abrupt rise in the skin β temperature of the tail.

Figure 1 shows the marked rise in skin tail temperature in response to nalmefene in doses as low as 10 ug/kg. Vet, as Figure ?, shows, an injection of 1000 ug/kg of nalmefene glucuronide had no effect.

Additional studies in rats using labelled nalmefene glucuronide demonstrated that nalmefene glucuronide is not absorbed to any measurable extent following oral administration of doses as high as 40 mg/kg. No radioactivity could be detected in plasma 2 hours after dosing while about 85* of the dose was present in the small intestine still as nalmefene glucuronide. However the 2-3* of the dose which had reached the cecum by this time was almost exclusively free nalmefene. Therefore the glucuronide of an opioid antagonist provides a means of preventing narcotic-induced intestinal hypomotility without interfering with central nervous system effects of narcotics, such as analgesia. e The glucuronide derivatives should be administered orally, preferably in the form of capsules or tablets. Known coating and tabletting agents can be used. As examples, known enteric coatings like polyacrylates and cellulose acetate phthalates may be used as coatings for the active i ngredient. The amount of glucuronide derivative administered at one time is from about 0.1 to 50 mg, preferably 0.5 - 20 mg.

The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention in the use r of such terms and expressions of excluding any equivalents of the features 30 shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

Claims (13)

1. The use of an opioid antagonist in the form of a glucuronide derivative having the formula: wherein Rj is = 0 or = CH 2 and R 2 is allyl or cyclopropylmethyl 15 in the manufacture of a composition for providing site specific opioid antagonism in the intestine of a subject without substantial systemic effects.

2. The use according to claim 1, wherein the glucuronide derivative 20 is selected from nalmefene-

3. G -D-glucuronide, naloxone-3β -D-glucuronide and naltrexone-3 β-D-glucuronide. 25 3. The use according to claim 2, wherein the glucuronide derivative is nalmefene-3β-D-glucuronide.

4. The use of an opioid antagonist in the form of a glucuronide derivative, having the formula: wherein is =0 or =CHg and Rg is allyl or cyclopropylmethyl in the manufacture of a pharmaceutical composition for the treatment of intestinal dysmotility in a subject suffering from an intestinal dysmotility, without substantial systemic effects, the amount of said glucuronide derivative being sufficient to provide opioid antagonism in the intestine of the subject, the glucuronide derivative undergoing cleavage in the intestine of the subject to assume the aglycone form of the antagonist.

5. The use according to claim 4, wherein the glucuronide derivative is selected from nalmefene-3 β-D-glucuronide, naloxone-3 β-D-glucuronide and naltrexone-3 β-D-glucuronide.

6. The use according to claim 5, wherein the glucuronide derivative is nalmefene-3 β-D-glucuronide.

7. A pharmaceutical composition in unit dosage form adapted for oral administration comprising a glucuronide derivative having the formula: wherein =0 or =CHg and Rg is allyl or cyclopropylmethyl and a pharmaceutically acceptable carrier for oral administration.

8. A pharmaceutical composition according to claim 7 wherein said unit dosage form is a capsule or tablet. 13

9. A pharmaceutical composition according to claim 7 wherein said composition is provided with an enteric coating.

10. A pharmaceutical composition according to claims 7 to 9 wherein each of said unit dosage forms comprises from about 0.1 to about 50mg, preferably 0.5 to 20mg of said glucuronide derivative.

11. A composition for site-specific delivery of an opioid antagonist to the intestine of a subject without substantial systemic effects, comprising nalmefene-3ρ -D-glucuronide or naltrexone-3ρ -D-glucuronide in an amount sufficient to provide opioid antagonism to the intestine of the subject and a pharmaceutically acceptable carrier for oral administration.

12. Use of an opioid antagonist as claimed in claim 1 substantially as described herein with reference to the Examples.

13. A pharmaceutical composition as claimed in claim 7 substantially as described herein with reference to the Examples.